Dynamics of Resolved Polar Clouds
The polar regions have been experiencing rapid warming and ice loss as greenhouse gas concentrations have risen. The projected warming in the Arctic varies significantly across climate models, part of which is attributed to polar cloud feedbacks. This thesis addresses the question of what drives the...
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California Institute of Technology
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ftdatacite:10.7907/69e7-0q10 2023-05-15T15:00:55+02:00 Dynamics of Resolved Polar Clouds Zhang, Xiyue 2018 PDF https://dx.doi.org/10.7907/69e7-0q10 https://resolver.caltech.edu/CaltechTHESIS:05312018-154833107 en eng California Institute of Technology No commercial reproduction, distribution, display or performance rights in this work are provided. Climate change Cloud dynamics Environmental Science and Engineering polar climate Thesis Text Dissertation thesis 2018 ftdatacite https://doi.org/10.7907/69e7-0q10 2021-11-05T12:55:41Z The polar regions have been experiencing rapid warming and ice loss as greenhouse gas concentrations have risen. The projected warming in the Arctic varies significantly across climate models, part of which is attributed to polar cloud feedbacks. This thesis addresses the question of what drives the changes in polar clouds as the climate warms, using a large eddy simulation (LES) model. LES is a powerful high-resolution model that resolves the most energetic turbulence relevant for clouds. First, we focus on the Arctic boundary layer clouds through three observation based case studies. The cloud and boundary layer characteristics simulated by the LES agree reasonably well with observations and model intercomparisons. We found that during polar night over sea ice, cloud water path increases with temperature and free-tropospheric relative humidity, but it decreases with inversion strength across the cloud top. Most of these changes can be explained by a mixed-layer model. The strength of the estimated positive cloud longwave feedback largely depends on the cloud top inversion strength. Next, we extend the LES domain to cover the entire polar troposphere, and use output from an idealized GCM as forcing to drive the LES. This novel framework allows changes in the large-scale circulation to be parameterized in the LES. The simulated seasonal cycle of liquid clouds resembles observations. In a warmer climate, there is a significant decrease of the low-level liquid clouds during summer and autumn. In spring and winter, liquid clouds increase at all levels. Both the liquid and ice cloud tops rise as the climate warms. Offline radiative transfer calculations estimate a positive cloud feedback that is dominated by longwave feedback. Thesis Arctic Climate change polar night Sea ice DataCite Metadata Store (German National Library of Science and Technology) Arctic |
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Open Polar |
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DataCite Metadata Store (German National Library of Science and Technology) |
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language |
English |
topic |
Climate change Cloud dynamics Environmental Science and Engineering polar climate |
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Climate change Cloud dynamics Environmental Science and Engineering polar climate Zhang, Xiyue Dynamics of Resolved Polar Clouds |
topic_facet |
Climate change Cloud dynamics Environmental Science and Engineering polar climate |
description |
The polar regions have been experiencing rapid warming and ice loss as greenhouse gas concentrations have risen. The projected warming in the Arctic varies significantly across climate models, part of which is attributed to polar cloud feedbacks. This thesis addresses the question of what drives the changes in polar clouds as the climate warms, using a large eddy simulation (LES) model. LES is a powerful high-resolution model that resolves the most energetic turbulence relevant for clouds. First, we focus on the Arctic boundary layer clouds through three observation based case studies. The cloud and boundary layer characteristics simulated by the LES agree reasonably well with observations and model intercomparisons. We found that during polar night over sea ice, cloud water path increases with temperature and free-tropospheric relative humidity, but it decreases with inversion strength across the cloud top. Most of these changes can be explained by a mixed-layer model. The strength of the estimated positive cloud longwave feedback largely depends on the cloud top inversion strength. Next, we extend the LES domain to cover the entire polar troposphere, and use output from an idealized GCM as forcing to drive the LES. This novel framework allows changes in the large-scale circulation to be parameterized in the LES. The simulated seasonal cycle of liquid clouds resembles observations. In a warmer climate, there is a significant decrease of the low-level liquid clouds during summer and autumn. In spring and winter, liquid clouds increase at all levels. Both the liquid and ice cloud tops rise as the climate warms. Offline radiative transfer calculations estimate a positive cloud feedback that is dominated by longwave feedback. |
format |
Thesis |
author |
Zhang, Xiyue |
author_facet |
Zhang, Xiyue |
author_sort |
Zhang, Xiyue |
title |
Dynamics of Resolved Polar Clouds |
title_short |
Dynamics of Resolved Polar Clouds |
title_full |
Dynamics of Resolved Polar Clouds |
title_fullStr |
Dynamics of Resolved Polar Clouds |
title_full_unstemmed |
Dynamics of Resolved Polar Clouds |
title_sort |
dynamics of resolved polar clouds |
publisher |
California Institute of Technology |
publishDate |
2018 |
url |
https://dx.doi.org/10.7907/69e7-0q10 https://resolver.caltech.edu/CaltechTHESIS:05312018-154833107 |
geographic |
Arctic |
geographic_facet |
Arctic |
genre |
Arctic Climate change polar night Sea ice |
genre_facet |
Arctic Climate change polar night Sea ice |
op_rights |
No commercial reproduction, distribution, display or performance rights in this work are provided. |
op_doi |
https://doi.org/10.7907/69e7-0q10 |
_version_ |
1766332957270736896 |